Device for reducing emissions in a vehicle combustion engine

ABSTRACT

A combustion chamber in an engine includes a piston and an injector with plurality of orifices arranged to inject spray/flame plumes, which impinge on a piston outer bowl section during most of the injection. Between spray/flame plume impingement areas and in a plane substantially perpendicular to reciprocal piston movement are arranged a first type of protrusions protruding into the combustion chamber, having a smooth form for preserving kinetic energy in the flame and for redirecting circumferential flame progress mainly towards a center axis of the piston with minimal flame-to-flame interaction. A second type of protrusions are arranged in the impingement areas, being adapted for redirecting flame progress into a circumferential flame progress direction in a plane substantially perpendicular to the reciprocal piston movement and with minimal flame-to-piston wall interaction and minimal kinetic energy loss.

BACKGROUND AND SUMMARY

The present invention relates to a device for controlling the combustionprocess in a combustion engine. The invention especially relates to sucha device for reducing especially soot emissions but also carbon monoxideand hydrocarbon in combustion engines in which the fuel/cylinder gasmixture is ignited by compression heat generated in the cylinder.

Soot particles (or particulates) are a product which, during combustion,can both be formed and subsequently oxidized into carbon dioxide (CO₂).The quantity of soot particles measured in the exhaust gases is the netdifference between formed soot and oxidized soot. The process is verycomplicated. Combustion with fuel-rich, fuel/air mixture with poormixing at high temperature produces high soot formation. If the formedsoot particles can be brought together with oxidizing substances such asoxygen atoms (O), oxygen molecules (O₂), hydroxide (OH) at sufficientlyhigh temperature for a good oxidation rate, then a greater part of thesoot particles can be oxidized. In a diesel engine, the oxidationprocess is considered to be in the same order of magnitude as theformation, which means that net soot production is the differencebetween formed quantity of soot and oxidized quantity of soot. The netemission of soot can therefore be influenced firstly by reducing theformation of soot and secondly by increasing the oxidation of soot.Carbon monoxide emissions (CO) and hydrocarbon emissions (HC) arenormally very low from a diesel engine. Yet the percentages can rise ifunburnt fuel ends up in relatively cool regions. Such regions are, inparticular, zones with intense cooling located close to the cylinderwall. Another example is cavities between piston and cylinder lining.

Nitrogen oxides (NOx) are formed from the nitrogen content in the air ina thermal process which has a strong temperature dependency and dependson the size of the heated-up volume and the duration of the process.

A combustion process in which the fuel is injected directly into thecylinder and is ignited by increased temperature and pressure in thecylinder is generally referred to as the diesel process. When the fuelis ignited in the cylinder, combustion gases present in the cylinderundergo turbulent mixing with the burning fuel, so that amixture-controlled diffusion flame is formed. The combustion of thefuel/gas mixture in the cylinder gives rise to heat generation, whichcauses the gas in the cylinder to expand and which hence causes thepiston to move in the cylinder. Depending on a number of parameters,such as the injection pressure of the fuel, the quantity of exhaustgases recirculated to the cylinder, the time of injection of the fueland the turbulence prevailing in the cylinder, different efficiency andengine emission values are obtained.

Below follows two examples of state of the art arrangements attemptingto lower both soot and NOx-emissions by controlling the flame, andtrying to brake the well known “trade off” between soot emissions andnitrogen oxide emissions, which is typical of the diesel engine, andwhich “trade-off” is difficult to influence. The majority of measureswhich reduce soot emissions increase the nitrogen oxide emissions.

EP1216347 shows an arrangement for controlling the combustion process ina combustion engine by controlling the combustion flame, with thepurpose to decrease soot and NOx emissions. The fuel is injected intothe combustion chamber with a sufficiently high kinetic energy (highinjection pressure) so as to supply kinetic energy to the spray in suchway that a spray-internal mixing process and a large-scale global mixingprocess between fuel and cylinder gas is achieved, thus keeping the sootemissions below a selected level. A proportion of recirculated exhaustgas is selected such that the nitrogen oxide emissions are kept below aselected level.

U.S. Pat. No. 6,732,703 shows an arrangement for minimizing NOxemissions and soot particulates. Here, the fuel spray hits inner bowlfloor section during injection in order to cool down the combustion andthereby decreasing the creation of NOx. The fuel is injected with highpressure and the piston is shaped to maintain the momentum in the sprayplume/flame and fuel/air mixture so that good mixing of available oxygenand soot occurs late in the combustion process. A lot of the momentum islost when the spray plume hits the inner bowl floor section and when twoadjacent flames hit each other during circumferential flame progress.

U.S. Pat. No. 5,215,052 discloses an arrangement for improved mixture offuel/air and decreased flow loss of flame expansion in a circumferentialdirection in the combustion space.

This is done by providing a piston with a shallow piston recess, anddepressions in the recess bottom so that they have a corrugated shape inrelation to the circumferential direction of the piston recess, andmainly in a plane perpendicular to the reciprocal movement of thepiston. Still a lot of momentum will be lost when the flame progressesin a circumferential direction that is perpendicular to the reciprocalmovement of the piston. This arrangement is not adapted for enhancedlate soot oxidation.

JP59010733 discloses a combustion chamber 8 with protrusions 10 at thetop of and inside the piston bowl. There is one protrusion for eachspray. Each fuel spray aims at its protrusion as to increase the flowspeed of the spray along the circumferential wall of the piston bowlwhen it is dashed against the protrusion. A lot of the momentum is lostespecially when adjacent flames hit each other during circumferentialflame progress.

Due to coming future emission legislation for combustion engines thereis a need to further lower the soot emission levels in order to meetcoming demands.

It is, therefore, desirable to overcome the deficiencies of the priorart and to provide an internal combustion engine containing a combustionchamber arrangement designed to reduce undesirable soot emissionssufficiently to meet new regulated limits. Thus, it is desirable tominimize the amount of soot by promoting efficient flame recirculationand thereby “saving” mixing energy to the final oxidation of soot andremaining fuel. The soot reduction is especially important for fuelssuch as for example diesel. It is also desirable to contribute to thereduction of carbon monoxide (CO) emissions and hydrocarbon (HC)emissions. The reduction of CO and HC becomes especially important forfuels such as for example DME (dimethyl ether).

It is also desirable to provide an engine wherein the shape, positionand dimensions of various features of the combustion chamberarrangement, cause the spray/flame to impinge upon and contact thepiston bowl surface in the outer bowl section and in order to optimizepreservation of kinetic energy in flame movements, mainly directed in aplane perpendicular to the reciprocal movement of the piston.

It is also desirable to provide a diesel engine capable of operate withsignificant soot emission improvements compared to e.g. an US02-engine,while also satisfying mechanical design constraints for a commerciallyacceptable engine.

It is also desirable to provide an engine including a combustion chamberarrangement having dimensions and dimensional relationships to ensureoxidation of sufficient amount of soot during combustion to minimizesoot available for discharge to the exhaust system. This can be donewithout increasing the creation of NOx.

According to an aspect of the present invention, an engine with acombustion chamber is provided, comprising: an engine body including anengine cylinder, a cylinder head forming an inner surface of thecombustion chamber and at least one intake port; a piston positioned forreciprocal movement in said engine cylinder between a bottom dead centerposition and a top dead center position, said piston including a pistoncrown comprising an upper surface facing the combustion chamber, saidpiston crown containing a piston bowl formed by an outwardly openingcavity, said piston bowl comprising a projecting portion having a distalend and an inner bowl floor section extending downwardly at a positiveinner bowl floor angle from a plane perpendicular to an axis ofreciprocation of the piston, said piston bowl further comprising anoutwardly flared outer bowl section having a concave curvilinear shapein cross section; an injector mounted on the engine body adjacent saidprojecting portion of said piston bowl to inject fuel into thecombustion chamber with high injection pressure, said injectorcomprising a plurality of orifices arranged to form fuel spray plumes,which during progress become ignited flames that impinge withinpredetermined impingement areas on said outer bowl section. The aspectof the invention is characterized in that said impingement areas are inthe outer bowl section during most of the injection and in thatsubstantially half way between said impingement areas in the outer bowlsection and in a plane perpendicular to said reciprocal movement arearranged a first type of protrusions protruding into the combustionchamber and having a smooth form adapted for preserving kinetic energyin the flame and for redirecting circumferential flame progress mainlytowards a center axis of the piston with minimal flame-to-flameinteraction.

According to one embodiment of an aspect of the invention a second typeof protrusions are arranged in said impingement area. Said second typeof protrusions are adapted for redirecting flame progress directedtowards the impingement area mainly into a circumferential flameprogress direction in a plane substantially perpendicular to saidreciprocal movement and with minimal flame-to-piston wall interactionand minimal kinetic energy loss.

In a further developed embodiment of an aspect of the invention saidprotrusions has a shape of a longitudinal ridge that extends only in theouter bowl area in a plane substantially parallel to said reciprocalmovement of said piston. In another embodiment a cross-section,perpendicular to the extension of said ridge, of a top of said ridge isformed with a curved shape with a average radius that is at least 1/20of a piston bowl radius of said piston. According to another embodimentsaid first type of protrusions are protruding more into the combustionchamber compared to said second type of protrusions.

Said internal combustion engine can have a first impingement in saidimpingement area when start of injection and a second impingement pointin said impingement area when end of injection. Said ridge can beextended at least from a first position arranged in a first plane thatis common for said first impingement point and said first position, andup to a second position arranged in a second plane that is common forsaid second impingement point and said second position. Said first andsecond planes are perpendicular to the reciprocal movement of saidpiston.

In one further preferred embodiment of an aspect of the invention saidcentral axis is arranged to impinge said outer bowl section during thewhole injection.

In another further preferred embodiment of an aspect of the inventionsaid intake port is formed in the cylinder head for directing intake airinto the combustion chamber with no or low swirling effect duringoperation. In a further preferred embodiment of the invention saidswirling effect has a swirl ratio in the range of 0.0 to 0.7.

In another further preferred embodiment of an aspect of the invention ageometry of the inner bowl floor section in relation to the spray axisis arranged in such a way so that there is enough volume and distancebetween the inner bowl floor section and the spray axis (30) so thatdisturbing contact between the unignited nozzle near portion of thespray and the inner bowl section is avoided.

In another further preferred embodiment of an aspect of the inventionsaid injected fuel, when injected, is arranged to form a mixture withsaid intake air in said combustion chamber, and that said mixture selfignites when compressed by said piston.

In another further preferred embodiment of an aspect of the inventionsaid engine is arranged to add a predetermined portion of re-circulatedexhaust gas to said intake air, said portion being adapted so thatnitrogen oxide emissions emerging from said combustion are kept below aselected low level.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described in greater detail below withreference to the accompanying drawings which, for the purpose ofexemplification, shows further preferred embodiments of the inventionand also the technical background, and in which:

FIG. 1 diagrammatically shows a cut view of a piston and cylinder in acombustion engine of an embodiment of the invention.

FIG. 2 diagrammatically shows the right half of the piston in FIG. 1with reflection angle of the geometrical central axis of the spray.

FIG. 3 a diagrammatically shows a top view of the piston in FIG. 1 withspray/flame flows according to an embodiment of the invention. FIG. 3 bdiagrammatically shows an alternative embodiment of the embodiment inFIG. 3 a.

FIG. 4 a diagrammatically shows corresponding side view of thespray/flame flows in FIG. 3 a.

FIG. 4 b diagrammatically shows corresponding side view of thespray/flame flows in FIG. 3 b.

FIGS. 5 a to 5 i shows three-dimensionally and diagrammatically a pistonaccording to the invention with cylinder in nine different on-the-spotaccounts during a fuel injection and combustion sequence.

FIG. 6 shows a three dimensional view of the embodiment shown in FIGS. 3a and 4 a.

DETAILED DESCRIPTION

To understand the unique physical characteristics of combustion chamber7 according to the invention, attention is initially directed to FIGS. 1and 2 illustrating the various physical characteristics or parameterswhich are required to achieve the unexpected emission reductionadvantages of the present invention.

In FIG. 1, a diagrammatic view is shown of a combustion engine 1 whichis designed to work according to the diesel process. The engine 1comprises a cylinder 2 and a piston 3, which reciprocates in thecylinder 2 and is connected to a crankshaft 4 so that the piston 3 isset to reverse in the cylinder 2 at an upper and lower dead centreposition. As is also common, one end of the cylinder cavity is closed bya engine cylinder head 14. The piston 3 is provided in its upper surface5 with a piston bowl 6, which forms a combustion chamber 7, togetherwith inner surface 21 of a cylinder head 14 and walls of the cylinder 2.In the cylinder head 14 one or more induction ports 9 are arranged. Theconnection between a respective induction port 9 and the cylinder 2 canbe opened and closed with an induction valve 10 disposed in eachinduction port 9. Arranged in the cylinder head are also one or moreexhaust ports 11. The connection between a respective exhaust port 11and the cylinder 2 can be opened and closed with an exhaust valve 12disposed in each exhaust port 11. The opening and closing of valves 10and 11 may be achieved by a mechanical cam or hydraulic actuation systemor other motive system in carefully controlled time sequence with thereciprocal movement of piston 3.

In the cylinder head 14 there is disposed at least one fuel injector 13,through which fuel is injected into the cylinder 2 as a fuel spray sothat the fuel is mixed with gas compressed in the cylinder 2 to form afuel/gas mixture, which is ignited by compression heat generated in thecylinder 2. The ignited part of the spray forms a flame. Duringinjection a part of the spray closest to the injector with newlyinjected fuel has not yet started to burn. The fuel is preferablyinjected with a very high pressure. Injector 13 includes a plurality ofsmall injection orifices (not shown), formed in the lower end of anozzle assembly of the injector 13 for permitting the high pressure fuelto flow from a nozzle cavity of the injector 13 into the combustionchamber 7 with a very high pressure to induce thorough mixing of thefuel with the high temperature, compressed charge air within combustionchamber 7. It should be understood that injector 13 may be any type ofinjector capable of injecting high pressure fuel through a plurality ofinjector orifices into the combustion chamber 7 in the manner describedhereinbelow. Moreover, injector 13 may include a mechanically actuatedplunger housed within the injector body for creating the high pressureduring an advancement stroke of the plunger assembly. Alternatively, theinjector 13 may receive high pressure fuel from an upstream highpressure source such as in a pump-line-nozzle system including one ormore high pressure pumps and/or a high pressure accumulator and/or afuel distributor. The injector 13 may include an electronically actuatedinjection control valve which supplies high pressure fuel to the nozzlevalve assembly to open a nozzle valve element, or controls the drainingof high pressure fuel from the nozzle valve cavity to create a pressureimbalance on the nozzle valve element thereby causing the nozzle valveelement to open and close to form an injection event. For example, thenozzle valve element may be a conventional spring-biased closed nozzlevalve element actuated by fuel pressure. The fuel injector 13 ispreferably centrally disposed in the cylinder head so a geometricalcentral axis of the fuel injector coincide with a geometrical centralaxis 15 of the cylinder, which geometrical central axis also is an axisof reciprocation of the piston 3, as shown in FIG. 1.

The combustion engine 1 shown in FIG. 1 works according to thefour-stroke principle. The engine 1 preferably comprises a plurality ofcylinders 2, each provided with a piston 3, where each piston 3 isconnected to a common crankshaft 4 through a connecting rod and thuscausing the piston to reciprocate along a rectilinear path within thecylinder 2 as the engine crankshaft 4 rotates.

FIG. 1 illustrates the position of the piston 3 circa 45 degrees beforea top dead center (TDC) position. A TDC position is achieved when thecrankshaft is positioned to move the piston to the furthest mostposition away from the rotational axis of the crankshaft. In theconventional manner, the piston moves from the top dead center positionto a bottom dead center (BDC) position when advancing through intake andpower strokes. For purposes of this disclosure, the words “upward” and“upwardly” correspond to the direction away from the engine crankshaftand the words “down” and “downwardly” correspond to the direction towardthe crankshaft of the engine or bottom dead center position of thepiston.

At an uppermost, TDC position, piston 3 has just completed its upwardcompression stroke during which the charge air allowed to enter thecombustion chamber 7 from induction port 9 is compressed thereby raisingits temperature above the ignition temperature of the engine's fuel.This position is here considered as the 360 degrees position commencingthe expansion/combustion stroke of the complete 720 degrees four strokecycle of piston 3. The amount of charge air that is caused to enter thecombustion chambers may be increased by providing a pressure boost inthe engine's intake manifold. This pressure boost may be provided, forexample, by a turbocharger (not shown) driven by a turbine powered bythe engine's exhaust, or may be driven by the engine's crankshaft.

The engine of the present invention includes combustion chambercomponents and features sized, shaped and/or positioned relative to oneanother, as described hereinbelow, to advantageously reduce particulatematter (PM) to levels at or below new regulatory standards whilemaintaining acceptable fuel economy. The invention is especiallydirected to reduce soot emissions. Soot is one fraction of PM.

Preferably the overall dimensions, shape and/or relative positioning ofthe combustion chamber components and features are such that themomentum of the fuel spray/burning cylinder gas flame is preserved aslong as possible on its way from the injector in a slightly downward,direction following the shape of the inner floor bowl section 19 andouter bowl section 20, and further upwards until impingement with innersurface 21 of the cylinder head occurs, thus ensuring sufficientoxidation of soot later in the combustion event.

Further, the dimensions, shape and/or relative positioning of thecombustion chamber components and features are such that a predeterminedlevel of balance between vertical (mainly upward) and tangentialmomentum (directed in a plane perpendicular to the axis 15) of the fuelspray/flame is achieved. This balance is important to reach in order tobe able to achieve very low soot emission levels. Parameters controllingthe balance are selected such that the spray/flame after it has impingedthe outer bowl section 20 mainly directed in an upward direction towardsthe inner surface 21 of the cylinder head, in order to minimize loss ofmomentum.

Preferably, the vertical and tangential movements of the flame form afan-shaped pattern (see also FIG. 5 d, explained below) just afterimpingement with outer bowl section 20, where approximately ⅓ of theflame movements are directed upwardly, as indicated with Y in FIG. 4,and the rest are directed in a tangential (horizontal) direction, asindicated with X_(R) for the parts of the flame turning right and withX_(L) for the parts of the flame turning left as shown in FIGS. 3 a and3 b. This invention is particularly directed towards the enhancement ofthe redirection of the horizontal movements of the flame, i.e. when theflame changes direction from being directed towards the outer bowl tobeing directed in said tangential direction, and further the redirectionof the tangential movement to a movement directed toward the axis 15,which is seen from above in FIGS. 3 a and 3 b.

The dimensions, shape and/or relative positioning of the combustionchamber components and features as described hereinbelow results in acombustion chamber capable of forming, directing, controlling andcreating a pattern of injected fuel and most of all burningfuel/cylinder gas mix (flame) within the combustion chamber 7 duringboth the initial stages of fuel injection and during the initiation ofcombustion and expansion of the resulting gases during the power strokeof the piston 3 and after end of injection so as to achieve very highreduction of especially soot emissions, but also carbon monoxide andhydrocarbon.

More particularly, the upper portion of piston 3 may be referred to asthe piston crown 16. Piston crown 16 includes the upper surface 5partially forming combustion chamber 7 and a piston bowl 6 formed by anupwardly opening cavity. Piston bowl 6 includes a projecting portion 17preferably positioned at or near the center of bowl 6. Projectingportion 17 includes a distal end 18 positioned, in the preferredembodiment shown in FIG. 1, at the center of piston bowl 3 and thuspositioned along the axis of reciprocation 15 of piston 3. Projectingportion 17 also includes an inner bowl floor section 19 extending fromprojecting portion 17 downwardly at an inner bowl floor angle α from aplane perpendicular to the axis of reciprocation of piston 3 as shown inFIG. 1.

Piston bowl 6 also includes an upwardly flared outer bowl section 20having a generally concave curvilinear shape in diametric cross section.Outer bowl section 20 effectively shapes and directs the flow of thefuel/air mixture or flame within the combustion chamber, especially inthe upward direction (as shown best in FIG. 4).

FIG. 2 diagrammatically shows the right half of the bowl shape of thepiston in FIG. 1 with reflection angle γ of the geometrical central axis30 of the spray (below designated spray axis) and spray axis angle β(below designated spray angle). Outer bowl section 20 is designed with aparticular radius Ri and a particular location for a center of radiusCRi. Di further indicates the distance between the distal end 18 and thecrossing point C of the several spray axis in the injector 13. DistanceD2 indicates the duration of the injection and change/movement of sprayaxis impingement point during the downward movement of the piston 3. Theposition of start and end of D₂ is dependent on time duration (amount offuel to be injected) and timing of the injection. Start of injection isin the lower end of the distance D₂ and end of injection is in the upperend of the distance D₂. R₂ indicates a radius at the lip or edgeconnecting outer bowl 20 with the upper surface 5 of the piston 3.Center of radius R₂ is indicated CR₂. R₃ indicates piston bowl radius.While the general shape of the combustion chamber has antecedence in theprior art, it is the specific configuration, and more importantly, thecritical dimensions and dimensional relationships described hereinbelowwhich result in the improved functional performance of the presentinvention.

The value of the reflection angle during an injection is stronglydependent of the selection of several geometrical parameters, such asDi, Ri, β and piston bowl radius R₃, besides the injection timing andinjection duration.

According to the invention of the present application and as alreadyintroduced above FIGS. 3 a and 3 b disclose two preferred embodiments ofthe invention and where FIG. 3 a shows an embodiment with only a firsttype of protrusion 40 evenly distributed around the circumference of theouter bowl 6. Said first type of protrusions are arranged approximatelyhalfway between the impingement areas 41 of two adjacent flames (inFIGS. 3 a and 3 b indicated by the two biggest arrows).

In a preferred embodiment of the invention said first type ofprotrusions has a form of a ridge that extends in the verticaldirection, thus in FIGS. 3 a and 3 b the protrusions are seen in across-section from above. Said cross-section could form a horizontalline (not shown) in FIG. 2, where said horizontal line crosses throughimpingement area indicated by D₂ in FIG. 2. Thus, said first type ofprotrusions are arranged in the same horizontal plane as the impingementareas of the different flames. Preferably a ridge of the first type ofprotrusion extends in length corresponding to the length of animpingement area. Thus, said ridge of said first type of protrusionextends at least from a first position arranged in a first horizontalplane that is common for said first impingement point (lower end pointof distance D₂) and said first position, and up to a second positionarranged in a second horizontal plane that is common for said secondimpingement point (upper end point of distance D₂) and said secondposition. All mentioned planes are perpendicular to the reciprocalmovement of said piston 3 or geometrical central axis 15 of thecylinder.

Said protrusions, when seen in a cross-section as in FIG. 3 a or 3 b,could have different forms. In one embodiment the top of the ridge canbe more sharp (not shown). In another embodiment the end of the base ofthe ridge can be less sharp with a smoother transition between the ridgepart and the circular shape of the outer bowl section (not shown). Acombination of a sharper top of the ridge and smoother transition fromridge to circular shape of the outer bowl section is also possible (notshown). Each half of a width 43 of the base of a ridge can be extendedup to, for example, approximately ⅓ of a total spray sector distance 42along the circular shape of an outer bowl section.

FIG. 3 b shows an embodiment of the invention with said first type ofprotrusion and a second type of protrusion 50. Said second type ofprotrusion redirects the horizontal movement of the flame from adirection towards the outer bowl area (impingement area) to thetangential directions X_(R) and X_(L).

In one embodiment of the invention a cross-section perpendicular to theextension of said ridges of said first or second type of protrusiondisclose a top of said ridge that is formed with a curved shape with anaverage radius that is at least 1/20 of the piston bowl radius R₃. Theshape of one such cross section can be the result of severalmathematically defined curves.

In another embodiment of the invention said first type of protrusionsare protruding more into the combustion chamber 7 compared to saidsecond type of protrusions. The opposite is also possible, or that saidfirst and second type of protrusions are identical in size.

A top of a protrusion of said first or second type is the part thatprotrudes furthest into the combustion chamber 7. In one embodiment ofthe invention a top of said first type of protrusion is positioned halfway between said impingement area and along said distance D₂ when seenin a vertical direction. In another embodiment of the invention a top ofthe second type of protrusion is positioned in middle of an impingementand along said distance D₂.

An embodiment where only the second type of protrusions are present isalso possible.

As indicated before the fuel should be injected with a high injectionpressure. An example of average injection pressure interval is 300 to4000 bar, and in a further example embodiment the range may be 1500 to2500 bar. The injection pressure is an important parameter to ensurehigh momentum in the spray/flame flow throughout the movement along theinner bowl floor section, outer bowl flow section, impingement with theinner surface of the cylinder head and in particular the movements ofthe cylinder gas following the EOI.

Another combustion chamber parameter for controlling emissions is theswirl ratio of the air flow that is generated by the induction ports 9.The swirl ratio SR is a ratio of the tangential velocity of the airspinning around combustion chamber 7 divided by the engine speed. Thatis, the swirl ratio is a measure of the tangential motion of the air asit enters the engine cylinder from the induction ports 9 of the cylinderhead 14. Precisely, the term swirl ratio refers to the averagein-cylinder angular velocity of the air at intake valve closing dividedby the cylinder piston angular velocity. For example, an engine runningat 1800 rpm with a cylinder head generating an air motion with a swirlratio of 2 implies that the air in the cylinder at intake valve closingis rotating with an average angular velocity of 3600 rpm. The higher theswirl ratio, the greater the swirling effect of the air or air fuelmixture, while the lower the swirl ratio, the lower the swirling effect.The swirling effect is a generally tangential motion that uponcompression by piston 3 creates turbulence and assists in the combustionprocess.

According to an embodiment of the invention, to be able to ensurecontrol of the spray/flame movement during the whole combustion, themomentum created by the injection pressure should be disturbed as littleas possible. Thus, according to the invention low swirl is preferable tobe able to achieve maximum advantage of the present invention when theprotrusions of said first and second type are symmetrical as indicatedabove and in the figures. In this description a swirl below 1.0 isconsidered to be low swirl. The applicant has found that a swirl ratiobelow 0.7 is preferable, and even more preferable is a swirl ratio below0.5 and down to zero for the above described embodiments.

In further embodiment of the invention more swirl can be allowed. Insuch an embodiment the protrusions of first and second type are adaptedto a particular swirl range. The adaptation can be done by having a formof the protrusions (especially the top) that is swept to a certaindegree in the flowing direction of the swirl. Thus, such protrusions areasymmetrical.

Ri should be sufficiently large in order to create a curvature in outerbowl section 20 that strongly maintains the momentum in the spray/flame.Outer bowl section 20 is also designed to prevent excessive momentum inthe spray/flame in one or several directions which would cause thespray/flame to progress too much in a certain direction, compared toothers directions, causing undesirable stagnation of the spray/flame andthus leaving behind increased soot emissions. When dimensioning saidfirst and/or second type of protrusions prevention of excessive momentumin the spray/flame should also be considered.

As already indirectly mentioned above an important aspect involvesorienting the central axis of each orifice in a spray angle β measuredbetween a plane perpendicular to the axis of reciprocation of the pistonand a central axis 30 of each spray (FIG. 2) so that the spray axis 30impinges the outer bowl section 20 during at least a part of theinjection duration. The geometry of the inner bowl floor section 19 inrelation to the spray axis 30 is such that there is enough volume anddistance between the inner bowl floor section and the spray axis 30 sothat disturbing contact between the not ignited nozzle near portion ofthe spray and the inner bowl section is avoided. This action causesspray axis 30 to be directed toward outer bowl section 20 with minimalcontact with the inner bowl floor section, thus avoiding disturbing theignition of the spray. In this way contribution is made to maximize thepreserving of spray/flame momentum up to the spray/flame impinges theouter bowl section.

Another important combustion chamber parameter significantly affectingsoot emissions is the number of injection or spray orifices in theinjector 13. In accordance with an embodiment of the present invention,at least four injection orifices are used to deliver fuel to combustionchamber 7. For a truck size combustion engine preferably, five to seveninjection orifices can be used. Engines with bigger piston diameter haveroom for more orifices. The number of orifices is dependent of how closethe impingements points of two adjacent sprays comes to each other. Thenumber of injection orifices N is critical for creating the properbalance, mentioned above, between the vertical and tangential movementsof the spray/flame. If there are too many injection orifices thedistance between the different points of spray axis impingements (withthe outer bowl section) would become to close to each other so that asmooth turn around movement (recirculation) of the spray in a horizontalplane would be restraint, and the upward vertical movement could becometoo strong, which could result in spray/flame regions wheresubstantially all momentum is lost, thus the after oxidation of sootwould decrease. Another important parameter that effects there-circulation is fuelling rate.

In order to increase the understanding of the inventive spray/flamecontrol in horizontal plane FIGS. 5 a to 5 i shows three-dimensionallyand diagrammatically a piston 3 with cylinder 2 in nine differenton-the-spot accounts during a fuel injection and combustion sequence,i.e. from approximately 5 degrees before TDC to a time spot late in thecombustion sequence, i.e. long after TDC. Note that the protrusionsaccording to the invention are not included in FIGS. 5 a to 5 i. Thepurpose of these figures is to try to visualize the progress of twoadjacent flames. The beginning of a spray axis 30 of two adjacentpositioned sprays is indicated with a dotted line in FIGS. 5 a to 5 i.In order to increase the clarity of the FIGS. 5 a to 5 i only two ofseveral sprays are shown.

FIG. 5 a shows start of injection (SOD. There is a ignition delay, whichoccurs between SOI and ignition of the fuel. FIG. 5 b shows start ofcombustion (SOC). The white areas indicate burning cylinder gas flames.FIG. 5 c shows when the flames impinges the outer bowl section 20(FlameToWall). The direction of movement of the left flame(corresponding counts for the right flame) is indicated with an arrow.Thus, the flames move from injector 13 towards outer bowl section 20.FIG. 5 d shows when the flames meet one another (FlameToFlame). Thecollision is indicated by that two of the four arrows are pointing ateach other. An important balance between vertical and tangentialmovements can be achieved when the flames after first impingement withouter bowl section (FIG. 5 c) are spread in a sun fan-shaped pattern asindicated in FIG. 5 d. This is achieved by selecting combustion chamberparameters within predefined ranges. The vertical arrows in FIG. 5 dcorrespond to Y in FIGS. 4 a and 4 b, and the arrow pointing to theright in FIG. 5 d corresponds to X_(R) in FIG. 3 a or 3 b and finallythe arrow pointing to the left in FIG. 5 d corresponds to X_(L) in FIGS.3 a and 3 b.

FIG. 5 e shows when the flames impinge the inner surface of the cylinderhead 21 (FlameToHead). This is indicated by a dotted area in the flames.Within said dotted area the flames are in contact with the inner surface21 of the cylinder head 14. The two arrows in the left flame indicatethe main movements of the flames along said inner surface 21. FIG. 5 fshows the important flame re-circulation, which is forced by theFlameToHead and FlameToFlame interaction and which is a result of mainlyselecting combustion chamber parameters within predefined ranges so thatsaid balance between vertical and tangential flame movements isachieved. The parameters deciding the dimensions of said protrusionsaccording to the invention are one of several parameters which can beused for flame control. A certain choice of said parameters controlstiming and position of said flame recirculation, shown especially inFIG. 5 f, but also in FIGS. 5 g to 5 i. The protrusions according to theinvention further enhance the positive effects of said flamere-circulation. Especially a symmetric FlametoFlame interaction createsuseful flame recirculation vortexes. The arrows indicate the directionof movement of the flame re-circulation, which are directed back intothe combustion chamber 7. The low swirl is here indirectly a reason formore intensive mixing thanks to symmetry-driven creation ofFlameToFlame-induced vortexes. With enough mixing energy (momentum)left, this flame recirculation contributes to mix and burn the lastinjected (and soot producing) fuel and thus also to oxidize soot late inthe combustion sequence. FIG. 5 g shows end of injection (EOI), thusmomentum from the injection pressure has ended and further movements ofthe cylinder gas depends mainly on earlier provided momentum from theinjection pressure. FIG. 5 h shows soot oxidation and spray dilutionafter EOI, due to powerful mix of the cylinder gases/flame.

FIG. 5 i shows late after burn rich pocket soot oxidation, which thecurrent invention is aiming at to increase with better control of thehorizontal spray/flame movements with the purpose to preserve momentumin the cylinder gases further, and thus as long as possible after EOI.

One important advantage of the invention is that enhanced lowtemperature soot after-oxidation can exist without significantnitrogenoxide (NOx) formation. The different embodiments of theinvention for reducing particulates/soot emissions can advantageously becombined with different known exhaust aftertreatment arrangements forreducing NOx, (and also soot traps) to lower the NOx-emissions evenfurther. The invention can advantageously also be combined with anexhaust gas recirculation (EGR) device, by which the level ofNOx-emissions can be controlled almost independently of theparticulates/soot emissions (see e.g. EP1216347).

Combinations of the above described combustion chamber parametersselected within specified ranges provide advantages in reducingsoot/particulates emissions in comparison to conventional enginedesigns, including specifically meeting new emissions standards relativeto especially soot. The inventive combustion chamber 7, besides thementioned inventive protrusions, specifically includes a positivereflection angle γ, low swirl and high injection pressure and thepositive effects of the invention can further be increased incombination with right selection of one or several of the other abovementioned parameters.

The present invention can be used in engines driven by fuels, such asfor example diesel, DME (dimethyl ether) or the like.

The invention presented can be applied on engines of passenger car sizeand up to an engine size of a big ship.

The invention should not be deemed to be limited to the embodimentsdescribed above, but rather a number of further variants andmodifications are conceivable within the scope of the following patentclaims.

The invention claimed is:
 1. An internal combustion engine with acombustion chamber, comprising: an engine body including an enginecylinder, a cylinder head forming an inner surface of the combustionchamber and at least one intake port; a piston positioned for reciprocalmovement in the engine cylinder between a bottom dead center positionand a top dead center position, the piston including a piston crowncomprising an upper surface facing the combustion chamber, the pistoncrown containing a piston bowl (6) formed by an outwardly openingcavity, the piston bowl comprising a projecting portion having a distalend and an inner bowl floor section extending downwardly at a positiveinner bowl floor angle (α) from a plane perpendicular to an axis ofreciprocation of the piston, the piston bowl further comprising anoutwardly flared outer bowl section having a concave curvilinear shapein cross section; an injector mounted on the engine body adjacent theprojecting portion of the piston bowl to inject fuel into the combustionchamber with high injection pressure, the injector comprising aplurality of orifices arranged to form fuel spray plumes, which duringprogress become ignited flames that impinge within predeterminedimpingement areas on the outer bowl section, wherein the impingementareas are in the outer bowl section during most of the injection and inthat substantially half way between the impingement areas in the outerbowl section and in a plane substantially perpendicular to thereciprocal movement are arranged a first type of protrusions protrudinginto the combustion chamber and having a smooth form adapted forpreserving kinetic energy in the flame and for redirectingcircumferential flame progress mainly towards a center axis of thepiston with minimal flame-to-flame interaction, and where each of theprotrusions has a shape of a longitudinal ridge that extends only in theouter bowl area in a plane substantially parallel to the reciprocalmovement.
 2. An internal combustion engine as in claim 1, wherein asecond type of protrusions are arranged in the impingement area, thesecond type of protrusions being adapted for redirecting flame progressdirected towards the impingement area mainly into a circumferential,flame progress direction in a plane substantially perpendicular to thereciprocal movement and with minimal flame-to-piston wall interactionand minimal kinetic energy loss.
 3. An internal combustion engine as inclaim 1, wherein a cross-section, perpendicular to the extension of theridge, of a top of the ridge is formed with a curved shape with anaverage radius that is at least 1/20 of a piston bowl radius (R3) of thepiston.
 4. An internal combustion engine as in claim 2, wherein thefirst type of protrusions are protruding more into the combustionchamber compared to the second type of protrusions.
 5. An internalcombustion engine as in claim 1 with a first impingement in theimpingement area when start of injection and a second impingement pointin the impingement area when end of injection, wherein the ridge isextended at least from a first position arranged in a first plane thatis common for the first impingement point and the first position, and upto a second position arranged in a second plane that is common for thesecond impingement paint and the second position, and where the firstand second planes are perpendicular to the reciprocal movement of thepiston.
 6. An internal combustion engine as in claim 1, wherein acentral axis (30) of the orifices is arranged to impinge the outer bowlsection during the whole injection.
 7. An internal combustion engine asin claim 1, wherein the intake port is formed in the cylinder head fordirecting intake air into the combustion chamber with no or low swirlingeffect during operation.
 8. An internal combustion engine as in claim 7,wherein the swirling effect resulting in a swirl ratio in the range of0.0 to 0.7.
 9. An internal combustion engine as in claim 1, wherein ageometry of the inner bowl floor section in relation to the spray axis(30) is arranged in such a way so that there is enough volume anddistance between the inner bowl floor section and the spray axis (30) sothat disturbing contact between the unignited nozzle near portion of thespray and the inner bowl section is avoided.
 10. An internal combustionengine as in claim 1, wherein the injected fuel, when injected, isarranged to form a mixture with the intake air in the combustionchamber, and that the mixture self ignites when compressed by thepiston.
 11. An internal combustion engine as in claim 1, wherein theengine is arranged to add a predetermined portion of recirculatedexhaust gas to the intake air, the portion being adapted so thatnitrogen oxide emissions emerging from the combustion are kept below aselected low level.